1. Field of the Invention
The present invention relates to a radio frequency (hereinafter, referred to simply as RF) receiving device of a mobile radio communication base station system in a CDMA (code division multiple access) system.
More particularly, the present invention relates to a control device for controlling power level between frequency assignment, in an RF receiving device of a mobile radio communication base station system in a CDMA system which down-converts an RF received signal into intermediate frequency signals for three frequency assignment, converts the down-converted three frequency assignment IF signals into digital signals, and executes a QPSK (quadrature phase shifting keying) demodulation and a channel filtering for each frequency assignment in a digital manner, whereby it prevents the performance deterioration of all channels due to the power level difference between the frequency assignment.
2. Discussion of Related Art
A general mobile radio communication base station system in a CDMA system includes a switching system and a cell equipment. Of course, the above system contains a large number of functional devices which are all embodied with various kinds of equipments.
The key part of the mobile radio communication base station system is composed of a channel card, a sector interface card, an analog common card and a digital shelf on which a terminal card is packaged. Additionally, it contains a tranceiver shelf which up-converts an IF signal outputted from the digital shelf in an ultra high frequency (UHF) signal and reversely, down-converts the UHF signal into the IF signal. In the tranceiver shelf the sector interface card is installed to couple baseband forward signals received from the channel cards and up-convert the coupled signal into the IF signal. The sector interface card receives the coupled baseband transmitting signals coupled from the analog common cards and couples and amplifies the received signals. The coupled signal is coupled, through a low-pass filter (LPF), to the IF signal, i.e., the delayed signal by the phase of 0xc2x0 and 90xc2x0 of 4.95 MHz and transmitted as the IF signal of 4.95 MHz, through a band-pass filter (BPF), to an RF rack. Therefore, the RF rack converts the received IF signal of 4.95 MHz into the UHF signal, for transmitting the converted signal through an antenna.
Now, an explanation of the construction and operation of the general mobile radio communication base station system will be discussed.
FIG. 1 is a block diagram illustrating the construction of a general mobile radio communication base station system. In construction, the system comprises: a base station control processor (BCP) 2 which operates and controls one base station; a base station interconnection network (BIN) 3 which serves as a packet router between the base station and a control station 1 via a line E1 or T1 and interfaces high-level data link control (HDLC) packet data between the processors within the base station; a time and frequency unit (TFU) 4 which generates a reference frequency and a timing synchronizing signal to thereby execute the synchronization for each processor within the base station and the timing synchronization with an adjacent base station; a digital unit (DU) 5 composed of a first digital unit 5a and a second digital unit 5b, which modulates/demodulates the data signal and voice signal transmitted/received through a CDMA channel; and an RF unit (RFU) 6 composed of a first RF unit 6a and a second RF unit 6b, which converts an UHF signal received from a mobile station into an IF signal to thereby transmit the converted IF signal to the digital unit 5, receives the IF signal inputted from the digital unit 5 to thereby convert the received IF signal into the UHF signal, and amplifies the converted UHF signal to a predetermined level to thereby execute space-radiation for the amplified UHF signal. The RF unit 6 is divided into an RF receiving device and an RF transmitting device.
Under the general mobile radio communication base station system in the CDMA system, the construction of a prior art RF receiving device is shown in FIG. 2.
As shown, the conventional RF receiving device includes an RF receiving antenna 10, a receiving unit 20, first to third RF down-converters 30, 31 and 32 by frequency assignment, first to third analog IF processors 40, 41 and 42 by frequency assignment, and first to third channel cards 50, 51 and 52 by frequency assignment.
The antenna 10 and the receiving unit 20 are used commonly for all frequency assignment and the first to third RF down-converters 30, 31 and 32 and the first to third analog IF processors 40, 41 and 42 are used by each frequency assignment. And, each of the first to third channel cards 50, 51 and 52 is used by one or more by frequency assignment. For instance, the RF receiving device in the CDMA system supporting four frequency assignment includes one antenna, one receiving unit, four RF down-converters, four analog IF processors, and four or more channel cards.
Now, an explanation of the operation of the prior art RF receiving device supporting the three frequency assignment will be discussed.
First, the receiving unit 20 receives the RF signal received from the antenna 10, limits the band of the received signal by using a band-pass filter (which is not shown in the drawing), amplifies the filtered signal to a predetermined level by means of a linear noise amplifier (which is not shown in the drawing), and outputs the amplified RF signal to the first to third down-converters 30, 31 and 32, respectively. The first to third down-converters 30, 31 and 32 receive the RF signal from the receiving unit 20, down-convert the received RF signals into IF signals by using two-stage mixer and local oscillator (which are not shown in the drawing), and output the down-converted frequency assignment IF signals to the first to third analog IF processors 40, 41 and 42. In other words, each of the first to third down-converters 30, 31 and 32 primarily down-converts the received RF signal into the IF signal of about 70 MHz through the local oscillator and mixer at the first stage and secondarily down-converts the received IF signal of 70 MHz into the IF signal of 4.95 MHz through the local oscillator and mixer at the second stage. At the same time, each of the first to third down-converters 30, 31 and 32 limits the band of the down-converted IF signal by using an SAW filter having the pass band of 1.25 MHz corresponding to the bandwidth of frequency assignment 1FA. The first to third analog IF processors 40, 41 and 42 receive the down-converted IF signals outputted from the first to third RF down-converters 30, 31 and 32, divide the received signals into the signals on I/Q channels to down-convert the signals on the I/Q channels into baseband signals, execute a quadrature phase shifting keying (QPSK) demodulation for each of the baseband signals, and convert the analog baseband signals on the I/Q channels into digital signals. And, the first to third analog IF processors 40, 41 and 42 execute multiplexing for the digital baseband signals on the I/Q channels and transmit the multiplexed signals to the first to third channel cards 50, 51 and 52. The first to third channel cards 50, 51 and 52 receive the multiplexed digital baseband signals on the I/Q channels by each frequency assignment and execute a CDMA demodulation for each of the received signals by the frequency assignment.
However, the above conventional RF receiving device of the mobile radio communication base station system in the CDMA system suffers from problems that the extension of system is carried out by one frequency assignment, because the RF down-converter and the analog IF processor are used by each frequency assignment, that the size of the base station system as well as the RF receiving device system is bulky, because three RF down-converters and three analog IF processors are required for processing the three frequency assignment, and that the expense increases, because of the large size.
To overcome these problems, another prior art digital RF receiving device of the mobile radio communication base station system in the CDMA system is shown in FIG. 3.
As shown, the above conventional digital RF receiving device includes: a receiving unit 20 for receiving the RF signal received via the antenna 10 from a mobile terminal device, limiting the band of the received signal, and amplifying the filtered signal to a predetermined level; an analog frequency down-converter 60 for down-converting the multi-carrier (three frequency assignment) RF signal outputted from the receiving unit 20 into arbitrary IF signals; and a digital frequency down-converter 70 for converting the IF signals for the three frequency assignment outputted from the analog frequency down-converter 60 into digital signals, dividing the converted digital signals into the signals on I/Q channels to down-convert the signals on the I/Q channels into baseband signals, and outputting the baseband signals on the I/Q channels by each frequency assignment to channel cards 50, 51 and 52 corresponding to each frequency assignment.
In the above construction, the analog frequency down-converter 60 comprises a local oscillator (which is not shown in the drawing) for generating an arbitrary local frequency, a mixer (which is not shown in the drawing) for mixing the local frequency generated in the local oscillator and the three frequency assignment RF signal to thereby output the three frequency assignment IF signal, and a wide band SAW filter (which is not shown in the drawing) for limiting the band of the three frequency assignment IF signal to the pass-band of the bandwidth corresponding to the three frequency assignment bandwidth. In this case, the IF is roughly 70 MHz and the bandwidth of the SAW filter is 3.75 MHz corresponding to the three frequency assignment. At this time, the reason why the bandwidth for the three frequency assignment is 3.75 MHz that the interval between the frequency assignment is 1.25 MHz. The digital frequency down-converter 70 comprises an A/D converter 71 for converting the band-limited IF signal outputted from the analog frequency down-converter 60 into the digital signal, a plurality of digital processors 72 to 74 for dividing the digital signal outputted from the A/D converter 71 into the signals on the I/Q channels by each frequency assignment, executing the QPSK demodulation for the divided I/Q channel signals and down-converting the demodulated signals into the baseband signals, and a multiplexor 75 for multiplexing the baseband signals on the I/Q channels for each frequency assignment outputted from the plurality of digital processors 72 to 74 to thereby output the multiplexed signals to the channel cards 50, 51 and 52 corresponding to the three frequency assignment. In this case, the baseband signals outputted from the digital processor 72 are the I/Q channel baseband signals for the frequency assignment 0FA, the baseband signals from the digital processor 73 are the I/Q channel baseband signals for the frequency assignment 1FA, and the baseband signals from the digital processor 72 are the I/Q channel baseband signals for the frequency assignment 2FA. At this time, each of the digital processors 72 to 74 comprises a channel divider (which is not shown in the drawing) for dividing the digital signal outputted from the A/D converter 71 into the I/Q channel signals, a local oscillator (which is not shown in the drawing) for generating an arbitrary local frequency, a mixer (which is not shown in the drawing) for mixing the local frequency generated in the local oscillator and each of the divided I/Q channel signals to thereby convert the mixed signal into the baseband signals on the I/Q channels, and a digital FIR filter (which is not shown in the drawing) for filtering the I/Q channel baseband signals by the frequency assignment outputted from the mixer and limiting the band of the filtered baseband signals to thereby output the band-limited baseband signals to the multiplexor 75.
Now, an explanation of the operation of the another prior art RF receiving device will be discussed.
First, the receiving unit 20 receives the three frequency assignment RF signal received from the antenna 10, limits the band of the received signal by using a band-pass filter provided therein, amplifies the filtered signal to a predetermined level by means of a linear noise amplifier (which is not shown in the drawing), and outputs the amplified RF signal to the analog frequency down-converter 60. The analog frequency down-converter 60 receives the RF signal from the receiving unit 20, down-converts the received RF signals into the IF signal of 70 MHz by using a mixer at a first stage, and outputs the down-converted frequency assignment IF signal to the A/D converter 71 of the digital frequency down-converter 70. In other words, if the three frequency assignment RF signal outputted from the receiving unit 20 is inputted to the mixer of the analog frequency down-converter 60, the mixer mixes the local frequency generated from the local oscillator and the three frequency assignment RF signal outputted from the receiving unit 20 and down-converts the mixed signal into the IF signal of 70 MHz. Then, the SAW filter, which has the pass-band of 3.75 MHz corresponding to the three frequency assignment, limits the band of the down-converted IF signal of 70 MHz and the band limited IF signal is outputted to the A/D converter 71 of the digital frequency down-converter 70. The IF signal outputted from the analog frequency down-converter 60 is converted into the digital signal in the A/D converter 71 of the digital frequency down-converter and then inputted to the three digital processors 72 to 74 for the three frequency assignment. Therefore, the digital processors 72, 73 and 74 execute the QPSK demodulation to divide the digital signals for the three frequency assignment into the I/Q channel signals and to down-convert the divided I/Q channel signals into the baseband signals on the I/Q channels. Then, the digital processors 72, 73 and 74 limit the band of the demodulated I/Q channel baseband signals for each frequency assignment through the digital FIR filter and output the I/Q channel baseband signals for each frequency assignment to the multiplexor 75. As a result, the digital processor 72 outputs the baseband signals on the I/Q channels for the frequency assignment 0FA, the digital processor 73 outputs the baseband signals on the I/Q channels for the frequency assignment 1FA, and the digital processor 74 outputs the baseband signals on the I/Q channels for the frequency assignment 2FA. Next, the multiplexor 75 executes the multiplexing for the baseband signals on the I/Q channels for the frequency assignment 0FA outputted from the digital processor 72 to thereby output the multiplexed signal to the channel card 50 for the frequency assignment 0FA, executes the multiplexing for the baseband signals on the I/Q channels for the frequency assignment 1FA outputted from the digital processor 73 to thereby output the multiplexed signal to the channel card 51 for the frequency assignment 1FA, and executes multiplexing for the baseband signals on the I/Q channels for the frequency assignment 2FA outputted from the digital processor 74 to thereby output the multiplexed signal to the channel card 52 for the frequency assignment 2FA. Each of the channel cards 50, 51 and 52 executes the CDMA demodulation for the inputted I/Q channel signals. As a result, the another prior art RF receiving device of the mobile radio communication base station system in the CDMA system replaces the plurality of RF down-converters and analog IF processors with the analog frequency down-converter 60 for outputting the IF signal of 70 MHz having the bandwidth corresponding to the multi-frequency assignment and the digital frequency down-converter 70 for converting the IF signal of 70 MHz into the digital signals through the A/D conversion, thereby making it possible to extend the frequency assignment by the multi-frequency assignment (three frequency assignment).
However, in the conventional RF receiving device where the multi-carrier (three frequency assignment) is processed at a time, when the power level difference by the frequency assignment is high due to the drastic variation of the subscribers or the generation of the spurious, as shown in FIG. 4a, the automatic gain control (AGC) in the analog frequency down-converter 60 does not operate normally. Since an AGC adjusting value in the AGC is calculated with the power level sensing value for the whole three frequency assignment, the frequency assignment signals having relatively low power level difference (the FA(1) and FA(2) in FIG. 4a) become disappear by the frequency assignment signal having a high power level difference (the FA(0) in FIG. 4a) through the AGC process. By estimating the signal power difference for each frequency assignment and by discriminating each frequency assignment, therefore, the AGC should be carried out. On the other hand, when the three frequency assignment signals exist after the AGC but the power level difference therebetween is generated, as shown in FIG. 4b, since the analog frequency down-converter 60 down-converts the signal having the three frequency assignment bandwidth (3.75 MHz), it is a possibility that a serious inter modulation distortion can be generated. The inter modulation distortion means that the frequency assignment signal having a relatively low power level (the FA(1) in FIG. 4b) to which the frequency assignment signals having relatively high power level (the FA(0) and FA(2) in FIG. 4b) flow becomes disappear. That is, in case where the high power level difference between the frequency assignment is generated, the performance deterioration for all channels is experienced. Therefore, there is a need to propose a new RF receiving device for preventing the performance deterioration for all channels caused due to the high power level difference between the frequency assignment.
An object of the invention is to provide a control device for controlling power level between frequency assignment in an RF receiving device of a mobile radio communication base station system in a CDMA system which is capable of lowering the power level of the frequency assignment signal having a relatively high power difference, if the power difference by the frequency assignment is high under the detection of the power level by the frequency assignment, to thereby minimize the power level difference between the frequency assignment, and then, executing an AGC process for the three frequency assignment, whereby the disappearance of the frequency assignment signal having a relatively low power difference caused by the frequency assignment having a high power difference can be prevented.
To accomplish this and other objects of the present invention, there is provided a control device for controlling power level between frequency assignment, in an RF receiving device of a mobile radio communication base station system in a CDMA system having an analog frequency down-converter for down-converting an RF signal outputted from a receiving unit into an IF signal and a digital frequency down-converter for converting the down-converted IF signal in the analog frequency down-converter into a digital IF signal and down-converting the digital IF signal into baseband signals for each frequency assignment to thereby output the baseband signals to corresponding channel cards, which comprises: a microcontroller for receiving the power level values for the baseband signals of each frequency assignment down-converted in the digital frequency down-converter to thereby determine a power level difference between the frequency assignment and selecting one frequency assignment signal having a relatively high power level difference to thereby generate an attenuation control signal attenuating the power of the selected frequency assignment signal; an IF analog processor for attenuating the power of the frequency assignment signal having the relatively high power level difference in the three frequency assignment signals obtained in the analog frequency down-converter in accordance with the attenuating control signal generated from the microcontroller and adding the IF signals for the frequency assignment to thereby output the added signal as the IF signal for the three frequency assignment; an automatic gain controller for determining an AGC value in accordance with the power level of the IF signals outputted from a plurality of digital processors for the frequency assignment within the digital frequency down-converter to thereby output the AGC value; and a gain controller for controlling the gain of the IF signals for the three frequency assignment outputted from the IF analog processor in accordance with the AGC value outputted from the automatic gain controller to thereby transmit the gain controlled three frequency assignment signal to the digital frequency down-converter.